Photo-sensitive composition

ABSTRACT

The invention pertains to a photo-sensitive composition which comprises a photochemical initiator, a polyacid or a salt thereof, and a poly(3,4-alkylenedioxythiophene) wherein the alkylene moiety is —(CH2)n- , n being an integer from 1 to 3, or 1,2-cyclo-hexylene, which may optionally be substituted, characterized in that the photochemical initiator is a water-soluble polymer comprising at least two azide or diazonium groups. Preferably, the water-soluble polymer is chemically stable at pH 6 or less, more preferably at pH 2 or less.

The invention pertains to a photo-sensitive composition comprising aphotochemical initiator, a polyacid or a salt thereof, and an organicconductor a method for making the photo-sensitive composition, the useof the photochemical initiator for cross-linking thepoly(3,4-alkylenedioxythiophene), and the use thereof for themanufacture of electrically conductive parts. Another aspect of theinvention pertains to an electronic component or a poly-LED comprisingthe said photo-sensitive composition.

Photo-sensitive composition comprising a photochemical initiator, apolyacid or a salt thereof, and a poly(3,4-alkylenedioxythiophene) areknown as organic conductor from WO 01/20691. In this patent applicationan electronic component is disclosed wherein the relief structurecontains a polyacid salt of a poly-3,4-alkylenedioxythiophene, in whichthe alkylene group is chosen from the group consisting of a methylene, a1,2-ethylene, a 1,3-propylene, and a 1,2 cyclohexene group, which groupsare optionally provided with one or more substituents, and wherein therelief structure comprises at least one electrode.

The stable conductivity of the component is achieved through the choiceof a specific electrically conductive salt of a specific group ofpoly(3,4-substituted thiophenes), which group of polythiophenes is alsocalled PEDOTs. The PEDOTs have a relatively high conductivity andconductivities higher than 100 S/cm have been disclosed, which isattributed to the oxygen substitutions at the 3,4-positions of thealkylene moiety of the poly(3,4-alkylenedioxythiophene).

The photochemical initiator that was used is the bisazide4,4′-diazidodibenzalacetone-2,2′-disulfonic acid disodium salt. Thiscompound initiates the crosslinking upon irradiation at a wavelength of360-370 nm. This is advantageous, as such a wavelength is provided by amercury lamp. Further, with initiators initiating the cross-linking uponirradiation at a shorter wavelength, such as less than 300 nm, theirradiation will probably influence the conductivity of the PEDOTs. Withinitiators initiating the cross-linking upon irradiation at a largerwavelength, such as more than 400 nm, the initiator initiates due tonormal light and the process should be executed in a dark room. Otherlowmolecular initiators, such as perchlorate, chromate and iron (III)tris(toluenesulfonate) were also disclosed and were assumed to bebrought into an excited state by irradiation, after which they act asstrong oxidizers towards the conjugated chain ofpoly-3,4-ethylenedioxythiophenes in the radiation-sensitive layer anddemolish the conjugation. A specific example is disodium chromate. Byheating to 150° C. after irradiation of the chromate-doped layer of apoly (styrene sulfonic acid) salt of PEDOT, the electrically conductivePEDOT can be made insoluble in water. The irradiated parts can besubsequently dissolved in water or some other polar solvent such as analcohol, so as to form the relief structure. The removal of the areasduring the developing step can be enhanced in a spray process.

These initiators, however, suffer from side reactions with oxygen and/orwith the present acid, and sometimes are not sufficiently stable underthe acid conditions of the polythiophene-polystyrene sulfonic acidmixture. A solution could be to increase the pH of the mixture, but suchincrease, for instance by the addition of a base, results in a decreaseof the conductivity of the resulting conductive parts. It was also foundthat high concentrations of initiator, and high doses were necessary toobtain acceptable conductive layers. It was further found that thechoice of the substrate was limited with this type of initiators, forinstance glass substrates could then not be used.

It is therefore an object of the invention to find photochemicalinitiators that do not suffer from the above disadvantages, are stableunder acidic conditions and show increased conductivity. Furtheradvantages such as improved relief structures with steeper walls andflatter upper-sides, lower concentrations of the initiator in thephoto-sensitive compositions, lower doses, better substratecompatibility, and intrinsic insensibility for oxygen become clear fromthe description and examples.

It was now found that of a new class of photoinitiators is very stableat lower pH, leading to highly conductive layers when applied in saidphoto-sensitive compositions, satisfy to the above-mentioned advantagesand furthermore retain all advantages of the prior art initiators. Theinvention therefore pertains to a photo-sensitive composition whichcomprises a photochemical initiator, a polyacid or a salt thereof, andan organic conductor characterized in that the photochemical initiatoris a water-soluble polymer comprising at least two azide or diazoniumgroups. The photo-sensitive composition is preferably chemically stableat pH 6 or less, more preferably at pH 2 or less.

The water-soluble polymer comprising at least two azide or diazoniumgroups can be a homo- or co-polymer. Suitable polymers comprise arepeating unit having the formula —[R(X—R₁)—], wherein X is an aromaticgroup-containing moiety, R₁ is an azide- or diazonium group attached tothe aromatic group of moiety X, and R is a substituted or unsubstitutedC1-C6 alkylene group, and with preference R₁ is the diazonium groupN₂₊A⁻, in which A⁻ is an inorganic or organic anion and X is—CONH—C₆H₄—. The (in)organic anion can be any suitable anion such ashalide among which chloride, hydrogen sulfate, tetrafluoro borate,hydrogen phosphate, thiocyanate, hexafluorophosphate, dodecylsulfate,and the like. When the alkylene group is substituted, the substituentmay be phenyl, halogen, hydroxy, and the like.

The aromatic group is preferably a phenyl group. The hydroxy group maybe etherified, esterified or, two hydroxy substituents may be ketalizedto form a cyclic structure. Such hydroxy group is suitable to use asanchor point for attaching moiety X, for instance through an ether orester linkage, or through a ketal group when two hydroxy groups arepresent in the repeating unit. Moiety X serves as a spacer between thebackbone of the repeating unit and the phenyl group to which the azideor diazonium group is attached. The precise chemical structure of thisspacer is not important and is usually determined by the simplicity ofthe chemical synthesis and the availability thereof. Esters and ketalsare less preferred because they may hydrolyze in strong acidic media,like the PEDOT/PSS latex.

The photo-sensitive compositions of the invention comprise polyacids,which are less vulnerable to attack by contaminating alkaline moleculesthan other organic and inorganic acids. Polyacids have a polymericstructure that appears to hamper diffusion of both the contaminatingalkaline molecules and the polyacids themselves. To benefit from theadvantages of WO 01/20691 it is preferred to use a component of the kinddescribed therein, which has a stable conductivity.

Examples of polyacids include poly(styrene sulfonic acid), polyacrylicacid, polymethacrylic acid, poly(vinyl sulfonic acid), poly(vinylsulfuric acid), poly(vinyl boric acid), poly(styrene boric acid),poly(vinyl phosphoric acid), poly(styrene phosphoric acid), poly(C1-C12alkyl sulfonic acid substituted ethylenedioxythiophene), poly(C1-C12alkoxy sulfonic acid substituted ethylenedioxythiophene). The polyacidcan further be a copolymer of a conductive polymer and a polyacid,wherein the chain comprises blocks of conductive units, for example of aPEDOT, and blocks of acid units.

Examples of substitutions optionally present at the alkylene groups areC1-C12 alkyl groups, C1-C12 alkoxy groups, phenyl groups, acid groups,such as sulfonic acid, carboxylic acid, boric acid and sulfuric acid,acid substituted C1-C12 alkyl-and C1-C12 alkoxy groups. Thesubstitutions can be used for several objects, such as to influence thesolubility of the organic conductor in different solvents, and toprovide a structure giving a higher order in the relief structure.

Examples of organic conductors include the PEDOTs i.e.poly(3,4-alkylenedioxythiophene) wherein the alkylene moiety is—(CH₂)_(n)—, n being an integer from 1 to 3, or 1,2-cyclohexylene, whichmay optionally be substituted, polyaniline, polypyrrole, polyactylene,among others, that may be substituted with alkylgroups, alkoxygroups,and the like, the substituents having a chain length of 1-12 carbonatoms for instance. Also ring shaped, aralkyl and alkaryl substituentscan be present. It is preferred to use the PEDOTs. The polyacid PEDOTsalt has a very high stability against bases. This is advantageous fromthe perspective of the manufacture or electronic components, such asintegrated circuits, as organic insulators have often a basic character,or are applied with a basic solvents. It is remarkable of this mannerstructuring the organic conductor, that it is broadly applicable.Diazonium compounds are known to have rather limited solybility in thepresence of organic sulphates. After filtering the composition, theconcentration of diazonium compounds is about 0.005% by weight (in theexamples). Apparently and surprisingly, this is sufficient to providethe relief structure. More important, it turns out to work for organicconductors as different as polyaniline and PEDOT.

The structure comprising a polyacid PEDOT salt may compriseinterconnects and resistors in addition to one or more electrodes. Theelectrodes may, for example, be part of a diode, a light-emitting diode,a bipolar transistor or a field-effect transistor. A clear advantage ofa component with an electrically conductive relief structure comprisinga polyacid salt of a PEDOT is the excellent stability of the reliefstructure and of the material when the structure is brought in contactwith, for example, organic and aqueous solvents, polymeric melts, ordeposited vapors. Relief structures containing a PEDOT salt are lessvulnerable to dissolution and to deterioration of their conductivity inalkaline solutions.

A layer on a substrate surface, which comprises a pattern of anelectrically conductive PEDOT is known from U.S. Pat. No. 5,447,824.This layer comprises conductive areas and less conductive areas.However, leakage currents taking place through the less conductive areashamper the use of the conductive areas as electrodes.

The component with an electrically conductive relief structure of a saltof a PEDOT may be realized by, for example, printing techniques such asmicrocontact printing, inkjet printing, and silkscreen printing.Lithographic techniques may alternatively be used, especially for themanufacture of tracks with relatively small track widths and relativelysmall distances between tracks.

In an embodiment of the component of the invention, the optionallypresent substitution contains a sulfonic acid. The acid can also bepresent as its acid anion. The extent to which the acid is present asits acid anion, presumably depends on the acidity of the solution, fromwhich the relief structure is formed. The advantage of such asubstitution is that the PEDOT itself is water-soluble beforecross-linking. In effect, the substitution gives the PEDOT an acidiccharacter, such that the PEDOT is to be considered as a polyacid itself.

Clearly, an additional polyacid is not absolutely needed in thisembodiment. An additional advantage is the increase of the amount ofPEDOT per cubic centimeter that is present in the relief structure ofthe component of the invention, which results in a better conductivity.In a further embodiment of the component of the invention, the reliefstructure comprises neighboring tracks, which lie at a distance of lessthan 10 μm from one another.

Such relief structures are suitable for use in integrated circuits. Inthis application neighboring tracks are used as parts of the source andthe drain electrode of a MOS-type field-effect transistor. The distancebetween neighboring tracks will be filled with semiconductor materialand will function as a channel. Hence, the distance between neighboringtracks is equal to the channel length cL. This has at least twoimportant implications. First, the switching speed of the transistor isdependent on the channel length. According to the theory of field-effecttransistors, this dependence is quadratic. With a channel length of lessthan 10 μm, it is possible to obtain bit rates of 1 kbit per second. Anintegrated circuit with such a bit rate is suited for use in datastorage and transponders. Besides, as is known from Brown et al.,Synthetic Metals 88 (1997), 37-55, a small channel length also leads toa high on-off ratio in the transistor, which is a measure for thequality of the transistor. Secondly, in order to have an integratedcircuit, there is not only the need of a small channel length, but alsothe need for ‘gain.’ The term ‘gain’ means that the output signal of atransistor or sets of coupled transistors such as NAND-, NOR-, AND-,OR-building blocks, has a voltage, which is as least as high as thevoltage of the input signal. It was found that with channel lengths ofless than 10 μm the gain is larger than 1.

In addition hereto, the conductive relief structures can be used indisplays, particularly for flexible or even rollable displays. Therelief structures are herein used as electrodes of the pixel transistorsand further as datalines. The conductivity of the relief structure issufficient for this use, even without strengthening the layer withmetal. In connection herewith, it is particularly advantageous to useelectrophoretic materials as the electro-optical layer in the display.

In a preferred embodiment of the component of the invention, theneighboring tracks are able to function as a pair of a source and adrain electrode. At least one of the tracks is furcate, having more thanone prong, while the electrodes are interdigitated. These electrodes arepositioned so as to enlarge the area of mutual exposure. This embodimentenlarges the source-drain current at a chosen drain voltage, and therebythe on/off ratio.

In another embodiment of the electronic component of the invention, thecomponent comprises a second relief structure of an electricallyconductive material, separated from said first relief structure at leastby an insulating layer. The second relief structure prevents leakagecurrents between tracks in use as interconnects and between tracks inuse as electrodes in different transistors, diodes, and capacitors.

In a preferred embodiment, the second relief structure also comprises asalt of a PEDOT.

In a further embodiment, the component of the invention comprises afield effect transistor. Such a transistor contains a source and a drainelectrode, which are interconnected through a channel comprising asemiconducting material. It further comprises a gate electrode, which isseparated from the source and the drain electrode by at least aninsulating layer. In this embodiment one, relief structure of thecomponent contains the source and the drain electrode. Preferably, theseelectrodes interdigitate in order to enlarge 30 the channel width.Another relief structure contains the gate electrode. At least one ofsaid relief structures is the relief structure comprising a salt of aPEDOT. The other, second electrically conductive relief structurecomprises a salt of a PEDOT, a polyaniline, silicon, or a metal such asgold. As is known in the art of transistor manufacture, differentdesigns are possible, such as a ‘top-gate’ design and a ‘bottom-gate’design.

In another embodiment of the component of the invention, the salt of thePEDOT is a polyacid salt. Poly(styrene sulfonic acid) is a preferredpolyacid.

In a further embodiment, not only the first relief structure, but thecomplete component substantially consists of polymeric material. Such“all-polymeric” device has favorable properties, such as a highmechanical flexibility and a low weight. Besides, the component ischeap, and hazardous substances may easily be avoided during itsmanufacture.

Organic materials for the semiconductor layer are known from WO99/10939. Examples include polypyrroles, polyphenylenes, polythiophenes,polyphenylene-vinylenes, polythienylene-vinylenes, poly(di)acetylenes,polyfuranes, polyfuranylenevinylenes, polyanilines. Alternatively,substituted derivatives of these polymers are applied.

Examples of substituents are alkyl and alkoxy groups and ring-shapedgroups, such as alkylenedioxy groups. By preference, the substituentgroups have a carbon chain of 1 to carbon atoms. As is known to thoseskilled in the art, such materials may be rendered semiconducting bydoping with, for example, an oxidizing agent, a reducing agent, and/oran acid. A preferred choice of an organic material ispolythienylene-vinylene. Oligomers such as pentacene may also be used asorganic semiconductor material.

Organic materials for the insulating layer are known from U.S. Pat. No.5,347,144. Examples include polyvinyl phenol, polyvinyl alcohol andcyanoethyl pullane. Preferably, an insulating material with a dielectricconstant of at least six is used, such as polyvinyl phenol, which can berendered insoluble by cross-linking with a cross-linking agent such ashexamethoxymethylene melamine and heating.

Substrate materials are, for example, polymers such as polystyrene,polyimide, polyamide, and polyester, or glass, ceramics, or silica.

The object relating to the method is achieved in that the method ofmanufacturing a relief structure on a substrate comprises the steps offorming a radiationsensitive composition which comprises thephotochemical initiator of this invention, a salt of an anion of apolyacid, and a poly-3,4-alkylenedioxythiophene, in which the alkylenegroup is chosen from the group consisting of an methylene group, a1,2-ethylene group, a 1,3 propylene group, and a 1,2-cyclohexylenegroup, which groups are optionally substituted;

-   -   providing said radiation-sensitive composition onto the        substrate so as to form a layer;    -   irradiating said layer in accordance with a desired pattern,        thereby obtaining irradiated areas and non-irradiated areas; and        developing said layer so as to form the electrically conductive        relief structure in the desired pattern.

The object relating to the method contains three elements: themanufacture of tracks with stable conductivity, the manufacture ofcomponents with narrow tracks, and lowcost manufacture. The stableconductivity is realized in that the composition used in the methodaccording to the invention comprises a salt of a PEDOT. Such acomposition is commercially available, but it was not known that thiscomposition could be applied in the manufacture of electricallyconductive relief structures. U.S. Pat. No. 5,300,575 teaches the use ofthis composition to provide an anti-static layer only.

The narrow tracks can be obtained by the use of a salt of a PEDOTcontaining a polyacid anion as a counter-ion, hereinafter also referredto as a polyacid salt. This polyacid salt substantially enhances theprocessability of the PEDOT. As a polyacid is soluble in polar solventssuch as water, the polyacid salt of the PEDOT is also more or lesssoluble in water or at least miscible with water. Through UV-irradiationof a layer of a polyacid salt of PEDOT in a desired pattern andsubsequently re-dissolving the salt, relief structures with track widthsand channel lengths of 10 μm can be obtained. In the art of plasticelectronics, such tracks may be called narrow.

The low-cost manufacture is realized in that it is not necessary to useresist layers, and in that water can be used as a solvent. The layer ispreferably washed with water in the developing step.

In the method of the invention, the radiation-sensitive layer can beapplied onto a substrate by spin-coating, web-coating, or electricaldeposition of a solution or dispersion and a subsequent removal of thesolvent or dispersion agent. The irradiation used may be UV-irradiationwith a photomask, or laser light, electron, X-ray, or ion-beams.Irradiation influences the initiator present.

The initiators of the invention are assumed to initiate cross-linkingbetweenpolymeric molecules in the radiation sensitive layers. In theinitiating process, the initiator molecules do react away. With suchinitiators, the non-irradiated areas are not cross-linked and will bewashed away. It is therefore another object of the invention to use thephotochemical initiator for cross-linking apoly(3,4-alkylenedioxythiophene) wherein the alkylene moiety is—(CH₂)_(n)—, n being an integer from 1 to 3, or 1,2-cyclohexylene, whichmay optionally be substituted, characterized in that the photochemicalinitiator is a water-soluble polymer comprising at least two azide ordiazonium groups, for instance for the manufacture of electricallyconductive parts in plastic conductors for electronic components and inpolymeric light emitting diodes (poly-LED's).

In another object of the invention there is provided in an electroniccomponent or a poly-LED comprising an electrically conductive reliefstructure 3 comprising at least one electrode on a surface of anelectrically insulating substrate 2, characterized in that theelectrically conductive relief structure 3 is obtainable by thecross-linking reaction of a poly(3,4-alkylenedioxythiophene) wherein thealkylene moiety is —(CH₂)_(n)—, n being an integer from 1 to 3, or1,2-cyclohexylene, which may optionally be substituted, in the presenceof a photochemical initiator, which is a water-soluble polymercomprising at least two azide or diazonium groups.

In a preferred embodiment of the method of the invention, thecomposition comprising the polyacid salt of the PEDOT is filtratedbefore application on the substrate. Preferably, a filter having poreswith a diameter of 5 μm or less is used in the filtration. Thefiltration prevents the eventual presence of particles larger than thewidths of the tracks formed.

In a further embodiment of the method of the invention, the electricalconductivity of the relief structure is enhanced by an additional stepperformed after washing, in which step the relief structure is dopedwith an organic compound containing a first functional group selectedfrom dihydroxy, polyhydroxy, carboxyl, lactam and amide, sulfon,sulfoxy, phosphate, and urea. The enhancement of the electricalconductivity is unexpectedly large, while the relief structure is notdamaged or demolished. The inventors tentatively presume, without beingbound by it, that the doping with said organic compound provides achange in the microstructure of at least part of the relief structure.Besides, the inventors have the impression that the doping after washingis very efficient: first, the solvent of the composition comprising aPEDOT salt has been removed at least for a major part at that moment.Molecules of the added organic compounds will interact with thepolymeric molecules mainly. Secondly, the surface area of the reliefstructure is larger than the surface area of the layer. The distributionof the organic compound may be assumed to be reasonably good.

Suitable organic compounds containing dihydroxy or polyhydroxy, and/orcarboxyl groups or amide groups are disclosed in WO 01/20691 and includesugar, sugar derivatives, and sugar alcohols, such as sucrose, glucose,fructose, lactose, sorbitol, mannitol and lactitol; alcohols such asethylene glycol, glycerol, di-or triethylene glycol; carboxylic acids,such as furancarboxylic acid. Particularly preferred organic compoundsare sorbitol and diethyleneglycol.

The following non-limiting examples illustrate the invention.

Procedure Used to Make Single Transistors and Logic

EMBODIMENT 1

The structural formula of the poly(styrene sulfonic acid) salt ofpoly-3,4-ethylenedioxythiophene is shown in FIG. 1. A composition ofthis salt in water is commercially available from Bayer. Theconcentration of PEDOT in this composition is 0.5% by weight and that ofpoly(styrene sulfonic acid) is 0.8% by weight. To the composition,apparently a colloidal solution, about 0.2% by weight of the diazoniumresin SCL 22S (the condensation product of 4-diazo-diphenylaminebisulfate and formaldehyde; Secant Chemicals Inc. MA USA) was added.After filtration through a 5 μm filter, the composition was spin coatedonto an insulating and planarized substrate. The layer obtained wasdried at 60° C. for 3 minutes. The dried layer was exposed through amask to patterned radiation with UV light (λ=365 nm) by means of an Hglamp. The layer was developed in a spray developer with water. In thisdeveloping step, the non-irradiated areas of the layer were removed.After drying at 200° C., the average layer thickness of the remainingareas was 80 nm. These areas had an electric conductivity of 1 S/cm.Each continuous undissolved area functions as a track. Track widths of1, 3, 5, 8, 10 and 20 μm and distances between tracks of 1, 3, 5, 8, 10and 20 μm were obtained in various experiments.

EMBODIMENT 2

The same procedure for obtaining relief structures was followed as inEmbodiment 1. However, after the washing and drying at room temperature,in which the relief structure comprising PEDOT was obtained on thesubstrate, a solution of sorbitol (about 4-6% by weight) was spin-coatedonto the relief structure. The resulting structure was heated to 200° C.The remaining areas had a conductivity of 170 S/cm. Each continuousundissolved area functions as a track.

EMBODIMENT 3

A solution of polyaniline and poly (styrene sulphonic acid) in aconcentration of 4.0 weight % is commercially available from Covion asPAT010. To this solution was added about 0.4% by weight of the abovementioned diazonium resin SCL 225. After filtration through 1 μm filter,the composition was spincoated on an insulating and planarizedsubstrate. The layer was dried at 60° C. during 3-5 minutes. It wasexposed through a mask to patterned radiation with UV light (λ=365 nm,intensity=10 W/cm²) during 20 seconds. The layer was developed in aspray developer with water. Track widths in the micrometer range from1-50 μm were obtained. The conductivity was in the order of 10 S/cm.This conductivity can be improved however through a suitable choice ofthe polyaniline from those commercially available.

EMBODIMENT 4

FIG. 2 diagrammatically shows a plan view of a field-effect transistor1, comprising conductive relief structures of the component according tothe invention. FIG. 3 diagrammatically shows the field-effect transistor1 in a cross-sectional view (not true to scale) taken on the line I-I ofFIG. 2. The field-effect transistor 1 comprises an electricallyinsulating substrate 2 of polyimide covered with a planarized layer ofpolyvinylphenol crosslinked with hexamethoxymethyl melamine, on which isprovided a first electrically conductive structure comprisingpoly(3,4-ethylenedioxythiophene), poly(styrene sulfonic acid) andsorbitol. The relief structure comprises a source electrode 34 and adrain electrode 35 with a track width tW of 5 μm. On the first reliefstructure a semiconductor layer 4 comprising poly(thienylene-vinylene)is provided, which layer 4 comprises a channel 41 (not indicated in FIG.3; shown in FIG. 2) with a channel length cL of 15 μm and a channelwidth cW of 50 μm. Covering the layer 4 and thus the channel 41 is anelectrically insulating layer 5 comprising the commercially availableHPR504, which is deposited as a solution in ethyl lactate. Itelectrically insulates the gate electrode 64 from the channel 41, saidgate electrode 64 being accommodated in the second electricallyconductive relief structure comprising PEDOT. The transistor is of the“top gate” type. The transistor may be protected against moisture andthe like by a protective layer, for instance a polycarbonate orpolyacrylate layer and the like, overlaying the second electricallyconductive relief structure and covering the total transistor.

EMBODIMENT 5

FIG. 4 diagrammatically shows a plan view of a field-effect transistor11, which comprises a first relief structure 3 comprisingpoly(3,4-ethylenedioxythiophene), poly(styrene sulfonic acid) andsorbitol and accommodating an interdigitated pair of source electrode 31and a drain electrode 32. The substrate, the insulating layer and thesemiconductor are omitted from the drawing for reasons of clarity. Thesource electrode 31 is fork-shaped and comprises parallel tracks 311,312, 313, and 314. The drain electrode is fork-shaped and comprisestracks 321, 322, 323, and 324. In this example, each of the electrodes31, 32 comprises four tracks with a track width tW of 2 μm; however,this is neither necessary nor meant to be limiting. The source 31 anddrain electrode 32 are separated by a channel 141 with a channel lengthcL of 5 μm. The transistor 11 further comprises a second reliefstructure comprising poly(3,4-ethylenedioxythiophene), poly(styrenesulfonic acid) and sorbitol and accommodating electrical conductors 611and a gate electrode 61. The transistor is of a “bottom gate” type. Inthis type of transistors the second relief structures lies on thesubstrate, on which the dielectric layer, the first relief structure,and the semiconductor layer comprising pentacene are arranged in thatorder.

With these procedures the following devices were made:

-   -   Vertical interconnects with a contact resistance of 3.5 k.,    -   Transistors with a channel length down to 1 μm, having        off-currents of 10 pA and on-currents of 1 μA and having a        mobility up to 10⁻² cm₂/V.s,    -   Invertors with a gain>1 (important for ring oscillators),    -   Ring oscillators based on: −7 stage invertor with a frequency up        to 1.3 kHz at 25V        -   −7 stage 2 input NAND invertor with a frequency up to 400 Hz            at 15V 10

Examples of some water-soluble polymeric compounds containing eitherdiazonium or azide groups are:

1)

A product of Toyo Gosei Kogyo (Japan) TGK-AS-982)

Diazo resins as disclosed in M. P.Schmidt and R.Zahn, German Patent596731 (1934)3)

Polyacrylamides functionalized with an azide or diazonium containinggroup, e.g. U.S. Pat. Nos. 5,990,269 and 5,725,978.4)

Poly(styrene-maleic anhydride) copolymers functionalized with an azide.Hayashi et.al. Polymeric Materials Science and Engineering (1995), Vol.73, pp559-560.

1. A photo-sensitive composition which comprises a photochemicalinitiator, a polyacid or a salt thereof, and an organic conductorcharacterized in that the photochemical initiator is a water-solublepolymer comprising at least two azide or diazonium groups.
 2. Thephoto-sensitive composition of claim 1, wherein the organic conductor isa poly(3,4-alkylenedioxythiophene) wherein the alkylene moiety is—(CH₂)_(n)—, n being an integer from 1 to 3, or 1,2-cyclohexylene, whichmay optionally be substituted.
 3. The photo-sensitive composition ofclaim 1 wherein the water-soluble polymer is chemically stable at pH 6or less, preferably at pH 2 or less.
 4. The photo-sensitive compositionof claim 1 or 2 wherein the photochemical initiator is a water-solublepolymer comprising at least two azide or diazonium groups and arepeating unit having the formula —[R(X—R₁)—], wherein X is an aromaticgroup-containing moiety, R₁ is an azide- or diazonium group attached tothe aromatic group of moiety X, and R is a substituted or unsubstitutedC1-C6 alkylene group.
 5. The photo-sensitive composition of claim 4wherein the photochemical initiator is a water-soluble polymercomprising at least two azide or diazonium groups and a repeating unithaving the formula —[R—(X—R₁)—], wherein R is C₆H₄, R1 is the diazoniumgroup N₂₊A⁻, in which A⁻ is an inorganic or organic anion and X is—NH—C₆H₄—.
 6. A method for making the photo-sensitive composition of anyone of claims 2 to 5 wherein a photochemical initiator, a polyacid or asalt thereof, and a poly(3,4-alkylenedioxythiophene) wherein thealkylene moiety is —(CH₂)_(n)—, n being an integer from 1 to 3, or1,2-cyclohexylene, which may optionally be substituted are mixedtogether, characterized in that a water-soluble polymer comprising atleast two azide or diazonium groups is used as the photochemicalinitiator.
 7. Use of a photochemical initiator for cross-linking apoly(3,4-alkylenedioxythiophene) wherein the alkylene moiety is—(CH₂)_(n)—, n being an integer from 1 to 3, or 1,2-cyclohexylene, whichmay optionally be substituted, characterized in that the photochemicalinitiator is a water-soluble polymer comprising at least two azide ordiazonium groups.
 8. Use of the photo-sensitive composition of claim 1or 2 for the manufacture of electrically conductive parts in plasticconductors for electronic components and in polymeric light emittingdiodes (poly-LED's).
 9. An electronic component or a poly-LED comprisingan electrically conductive relief structure (3) comprising at least oneelectrode on a surface of an electrically insulating substrate (2),characterized in that the electrically conductive relief structure (3)is obtainable by the cross-linking reaction of an organic conductor inthe presence of a photochemical initiator, which is a watersolublepolymer comprising at least two azide or diazonium groups.
 10. Anelectronic component as claimed in claim 9, characterized in that theorganic conductor is a poly(3,4-alkylenedioxythiophene) wherein thealkylene moiety is —(CH₂)_(n)—, n being an integer from 1 to 3, or1,2-cyclohexylene, which may optionally be substituted.